364 KANSAS UNIVERSITY SCIENCE BULLETIN. 



chromosomes crowd together and, on account of the lagging of 

 the accessory, lateral views of this stage show the condition re- 

 produced in figures 25 and 26, plate LXVIII; (x) is the ac- 

 cessory. It is easily identified in both daughter groups. Fig- 

 ure 24 shows the only case observed which might be inter- 

 preted as the failure of the accessory to divide. The spherical 

 form of the structure (x) may indicate a degenerate form of 

 the accessory or an unusually persistent plasmasome. The 

 crowding together of the diads at the poles completes the cycle 

 of changes occurring during the first spermatocyte generation. 

 No telophase involving the disintegration of the chromosomes 

 and the appearance of a new nuclear membrane occurs. 



The Second Spermatocyte. 



The second spermatocyte generation begins with the forma- 

 tion of an equatorial plate by the members of the new sperma- 

 tocyte nucleus. These second spermatocyte chromosomes con- 

 sist of ten diads and one monad or single chromatid, the acces- 

 sory. In figures 1, 2, plate LXIX, of typical equatorial plates 

 of this generation will be seen a tendency toward the same 

 chromosome arrangement which prevailed during the preced- 

 ing mitotic cycle. From the size relations shown in figure 4, 

 plate LXIX, which is a group of accessory chromosomes from 

 cells of the same stage and animal as figure 3, plate LXIX, re- 

 spectively, we are justified in our conclusions as to the identity 

 of this element. Figures 5, 6 and 7, plate LXIX, are polar 

 views of beginning anaphases. The chromosomes are viewed 

 here in cross-section. Figures 10, 11 and 12, plate LXIX, show 

 lateral views of the beginning of this ultimate division. Figure 

 10 suggests what transpired between the stage shown in figures 

 1, 2 and 3 and that shown in figures 5, 6 and 7. The transi- 

 .tion is extremely brief, for evidence of it is comparatively in- 

 frequent. The chromatids which, during the first spermatocyte 

 division, lay parallel to each other have separated at one ex- 

 tremity and have swung around until they lie end to end, the 

 separate ends pointing toward opposite poles. The chromatids 

 maintain this position during a relatively long period of 

 time, for this condition and the following telophase are most 

 commonly noted in cysts of second spermatocytes. A typical 

 spindle is formed and the fibers are attached at the separated 

 ends of the chromatids. Separation of chromatids occurs 

 simultaneously, the smallest member here acting in unison 



